With adjusting devices, such as are used for electrically-operated window lifters or sliding roofs in motor vehicles, an anti-jamming system for limiting the excess force generated by the drive is described. The anti-jamming system detects the occurrence of jamming in that it compares the current determined adjusting force values at a predetermined position during an adjusting operation with a predetermined reference. If jamming is present, the movement of the closing part is stopped and, if necessary, the drive is reversed. The reference is formed by adjusting force comparison values, which are normally determined for each adjusting device by an initialization run at the end of production and stored in the form of a learning curve in a memory of the control device.
However, this learning curve is a weak point: the adjusting force comparison values on which the learning curve is based are no longer current soon after its initial use because the mechanical conditions of the adjusting device, especially friction forces and initial sluggishness, can change very rapidly at the start of the utilization phase. These changes are not detected during the initialization run. The consequences of this are that the anti-jamming system does not function at its best, especially at the start of utilization; if jamming occurs, a jamming force is effective which is greater or smaller than would have been necessary with a precise knowledge of the actual opposing mechanical forces. This is unsatisfactory with regard to the safety or stability of the adjusting device.
Furthermore, the recording of a learning curve, which has to be performed individually for each adjusting device, is associated with corresponding costs during manufacture.
In DE 196 33 941 A1, a motor vehicle servoactuator is proposed with which the adjusting device adapts to the changed condition of the mechanical system. For this purpose, a friction force-travel diagram, stored as a reference, is continuously updated during operation.
During updating, the problem arises that the rapidly changing condition of the mechanical system at the start of the service life has to be catered for. In other words, the speed of adaptation must be large. On the other hand, during later operation it is desirable in the event of a disturbance occurring only once, for example when the vehicle is driving on a poorly-paved road, for the adjusting force comparison data to be only slightly influenced. However, a low speed of adaptation is desirable for this purpose.